Based on NABP's policy, once you cancel your exam, you will forfeit the registration fee & need to start the whole process again...paying another $505 & waiting for your state board to get approval...etc.
I did experience the problem of not rescheduling w/in the 48 hrs per their policy & thus had to pay the $140 resitting fee. There isn't much you can do now beside reapplying and waiting for another ATT. Good luck!